Mink nghĩ đề này là phân tích đa thức thành nhân tử chứ k phải tìm x^^
a) \(x^2-x-56=x^2-8x+7x-56=x\left(x-8\right)+7\left(x-8\right)=\left(x+7\right)\left(x-8\right)\)
b) \(4x^4+1=\left(4x^4+4x^2+1\right)-4x^2=\left(2x^2+1\right)^2-\left(2x\right)^2\)
\(\left(2x^2+1-2x\right)\left(2x^2+1+2x\right)\)
c) \(5x^2-x-4=5x^2-5x+4x-4=5x\left(x-1\right)+4\left(x-1\right)=\left(x-1\right)\left(5x+4\right)\)
d) \(4x^4+81=\left(4x^4+36x^2+81\right)-36x^2=\left(2x^2+9\right)^2-\left(6x\right)^2\)
\(=\left(2x^2+9+6x\right)\left(2x^2+9-6x\right)\)
e) \(64x^4+y^4=\left(64x^4+16x^2y^2+y^4\right)-\left(4xy\right)^2=\left(8x^2+y^2\right)^2-\left(4xy\right)^2\)
\(=\left(8x^2+y^2-4xy\right)\left(8x^2+y^2+4xy\right)\)
a)\(x^2-x-56\)
\(=x^2+7x-8x-56\)
\(=x\left(x+7\right)-8\left(x+7\right)\)
\(=\left(x-8\right)\left(x+7\right)\)
b)\(4x^4+1\)
\(=\left(2x+1\right)^2-4x^2\)
\(=\left(2x^2-2x+1\right)\left(2x^2+2x+1\right)\)
c)\(5x^2-x-4\)
\(=5x^2+4x-5x-4\)
\(=x\left(5x+4\right)-\left(5x+4\right)\)
\(=\left(x-1\right)\left(5x+4\right)\)
d)\(4x^4+81\)
\(=\left(2x^2\right)^2+9^2+36x^2-36x^2\)
\(=\left(2x^2+9\right)^2-36x^2\)
\(=\left(2x^2-6x+9\right)\left(2x^2+6x+9\right)\)
e)\(64x^4+y^4\)
\(=\left(8x^2\right)^2+y^4+16x^2y^2-16x^2y^2\)
\(=\left(8x^2+y^2\right)^2-\left(4xy\right)^2\)
\(=\left(8x^2+y^2-4xy\right)\left(8x^2+y^2+4xy\right)\)
